The present invention relates to a dry end of a machine for the manufacture of a fiber web, and particularly a paper web. The dry end has a single wire dryer group followed by a twin wire dryer group. Such a dry end is part of a paper manufacturing machine which was placed in operation in 1989.
The present invention is concerned with threading the web to be dried into the dry end. In a known threading technique the mechanically dewatered web which is formed in the initial part of the paper manufacturing machine, i.e. in the wire and press sections, travels during the initial phase and usually already at its full intended operating speed, provisionally only up to the outlet end of the press section. From there, the web enters a broke pulper. While this is occurring, a narrow edge strip is cut from the web and is transferred into the dry end. When the leading tip or tail of the edge strip has reached the outlet end of the dry end, the edge strip is gradually widened until it reaches the full width of the web.
The known dry end includes at least one single wire dryer group in which the web travels together with a support belt, for instance, a dryer wire, alternately over dryer cylinders and deflecting rolls. In such a single wire dryer group, the web and thus also the leading tip of the edge strip travels over the dryer cylinders between the outer surfaces of the cylinders and the support belt, while over the deflecting rolls, the web travels on the outside of the support belt. In the region of the deflecting rolls, the web, including the leading tip of the edge strip, is held fast against the support belt by a vacuum in or at the deflecting rolls. However, special edge suction chambers can be provided in the deflecting rolls for holding the edge strip to those rolls. Furthermore, it is known to provide blast nozzles which contribute to guiding the leading tip of the edge strip.
After traveling through the single wire dryer group, the web enters a following twin wire dryer group. There the web travels alternately over upper and lower dryer cylinders arranged in respective upper and lower rows. The web is pressed by an upper support belt against all of the upper dryer cylinders and by a lower support belt against all of the lower dryer cylinders. On the path from an upper cylinder to the next lower cylinder and then to the next upper cylinder, the web travels a distance over which the web is free of any support belt and therefore the web travels in a so called open web length.
A rope guide for threading the tip of the edge strip is provided here, laterally outside the width of the web. This guide comprises two ropes which, along the same path as the web, travel alternately over the upper and lower dryer cylinders. The two ropes form a so called rope shears at the beginning of the twin wire dryer group. There the two ropes converge toward each other so that they can grasp the tip of the edge strip and transport it further. Shortly before or upstream of the rope shears, with respect to the direction of travel of the web, a deflection device deflects the leading tip of the edge strip from the lateral region of the width of the web laterally outward into the rope shears.
In the known dry end, the transfer from the last dryer cylinder of the single wire dryer group to the first dryer cylinder of the twin wire dryer group is developed similarly to the transfer shown in FIG. 1 of published International Application WO 83/00514, noting the two dryer cylinders 14 and 26. In practice, however, the first open length of the web between these two dryer cylinders is shortened in that the last deflecting roll 19 of the single wire dryer group and the first deflecting roll 28 of the twin wire dryer group are arranged at a relatively short distance apart. This is desirable in normal operation for dependable guidance of the web. This arrangement, however, has the following disadvantage. Since the rope shears is arranged in the vicinity of the point at which the web runs onto the first dryer cylinder of the twin wire dryer group, the above described deflection of the tip of the edge strip must be effected within a relatively short open length of the web. This affords difficulties, although a scraper having a guide plate, and which can be developed approximately in accordance with German Published Patent Application 39 41 242.3, is provided on the last dryer cylinder of the single wire dryer group for guiding the edge strip.